The LM567 is a general purpose tone decoders designed to provide a saturated transistor switch to ground when an input signal is present within the passband. The circuit consists of an I and Q detector driven by a voltage controlled oscillator which determines the center frequency of the decoder. External components are used to independently set center frequency, bandwidth and output delay.

Features:

•     20 to 1 frequency range with an external resistor
•     Logic compatible output with 100 mA current sinking capability
•     Bandwidth adjustable from 0 to 14%
•     High rejection of out of band signals and noise
•     Immunity to false signals
•     Highly stable center frequency
•     Center frequency adjustable from 0.01 Hz to 500 kHz der with open collector NPN transistor for driving relay.

Useful Documents:

1) Datasheet